We quantified the areal hypolimnetic mineralization rate (AHM; total areal hypolimnetic oxygen depletion including the formation of reduced substances) in two formerly eutrophic lakes based on 20 yr of water-column data collected during oligotrophication. The upward diffusion of reduced substances originating from the decomposition of organic matter in the sediment was determined from pore-water profiles and related to the time of deposition. More than 80% of AHM was due to degradation of organic matter in the water column (including sediment surface) and diffusion of reduced substances from sediment layers younger than 10 yr. Sediments older than 10 yr, including the eutrophic past, accounted for , 15% of AHM. This ‘‘old’’ contribution corresponds to a 20–43% fraction of the total sediment-based AHM. The contribution from old sediment layers to AHM is expected to be even lower in lakes with deeper hypolimnia (. 12 m). In summary, oxygen consumption in stratified hypolimnia is controlled mainly by the present lake productivity. As a result, technical lake management measures, such as oxygenation, artificial mixing, or sediment dredging, cannot efficiently decrease the flux of

The neurotoxin anatoxin-a (ATX), has been detected in several northeast German lakes during the last two decades, but no ATX producers have been identified in German water bodies so far. In 2007 and 2008, we analyzed phytoplankton composition and ATX concentration in Lake tolpsee (NE Germany) in order to identify ATX producers. Sixty-one Aphanizomenon spp. strains were isolated, morphologically and phylogenetically characterized, and tested for ATX production potential by liquid chromatography–tandem mass spectrometry (LC–MS/MS). New primers were specifically designed to identify a fragment of a polyketide synthase gene putatively involved in ATX synthesis and tested on all 61 Aphanizomenon spp. strains from L. Stolpsee and 92 non-ATX-producing Aphanizomenon spp., Anabaena spp. and Anabaenopsis spp. strains from German lakes Langersee, Melangsee and Scharmützelsee. As demonstrated by LC–MS/MS, ATX concentrations in L. Stolpsee were undetectable in 2007 and ranged from 0.01 to 0.12 µg l-1 in 2008. Fifty-nine of the 61 strains isolated were classified as Aphanizomenon gracile and two as Aphanizomenon issatschenkoi. One A. issatschenkoi strain was found to produce ATX at concentrations of 2354 ± 273 µg g-1 fresh weight, whereas the other A. issatschenkoi strain and A. gracile strains tested negative. The polyketide synthase gene putatively involved in ATX biosynthesis was found in the ATX-producing A. issatschenkoi strain from L. Stolpsee but not in the non-ATX-producing Aphanizomenon spp., Anabaena spp. and Anabaenopsis spp. strains from lakes Stolpsee, Langersee, Melangsee, and Scharmützelsee. This study is the first confirming A. issatschenkoi as an ATX producer in German water bodies.

A new method for the assessment of the filterability in membrane bioreactors was tested for five months in four MBR units in Berlin. The new method BFM (Berlin Filtration Method) for filterability assessment uses a small membrane filtration test cell which can be submerged directly in the biological tanks to determine the filterability of the activated sludge in-situ. The test cell contains an aerated flat-sheet membrane which operates at similar conditions as in the plant. Filterability is expressed in terms of critical flux obtained by performing flux-stepping experiments. The ultimate goal of monitoring the filterability with the device is to detect in real time fouling occurrences due to changes in sludge composition and to adapt accordingly the operating conditions. The usefulness of the device for this purpose was evaluated for five months after monitoring four MBR plants in Berlin with different activated sludge characteristics (MLSS from 5 to 21 g/L, SRT 12–35d and COD in the supernatant 30–400 mg/L). The first results show a good agreement between the filterability of the sludge with the portable filtration test cell and the filtration performance of the plant. Critical flux values varied between 3 and 30L/m2 h during the studied period. Useful information concerning the irreversibility of the fouling was provided by looking at the hysteresis curve of the flux-stepping experiments.

Management models for aquatic systems can be used to determine which measures in the watershed or in the water body have been effective and/or which one should be used in future. The newly developed management models presented in the following for Lake Tegel and Schlachtensee are empirical and lake specific. The values for the unknown factors are estimated by an iterative process using optimisation routines and sensitivity analysis methods. The resulting models describe the water and phosphorus balance of each lake. The Lake Tegel water balance model calculates the unknown water inflow from the River Havel depending on the other main in- and outflows with very good validation results. The phosphorus models of both lakes quantify mixing of the upper and lower water body as well as sedimentation and release from the sediment as functions of measured variables. For Lake Tegel, management scenarios were run indicating effective management interventions. For Lake Schlachtensee, the phosphorus model captured the variations in the hypolimnion well but produced poorer results for the epilimnion because of unknown external phosphorus loads. For these the model indicated possible sources and magnitudes.

Whilst the importance of integrated modelling of urban wastewater systems is ever increasing, there is still no concise procedure regarding how to carry out such modelling studies. After briefly discussing some earlier approaches, the guideline for integrated modelling developed by the Central European Simulation Research Group (HSG - Hochschulgruppe) is presented. This contribution suggests a six-step standardised procedure to integrated modelling. This commences with an analysis of the system and definition of objectives and criteria, covers selection of modelling approaches, analysis of data availability, calibration and validation and also includes the steps of scenario analysis and reporting. Recent research findings as well as experience gained from several application projects from Central Europe have been integrated in this guideline.

Three different methods for fi ltration characterization in Membrane Bioreactor (MBR) systems were compared. These were the Delft Filtration Characterization Method (DFCm), the Berlin Filtration Method (BFM) and an ex situ side-stream fi ltration test cell for the determination of the critical fl ux. The ex situ fi ltration test cell and the DFCm fi lter activated sludge from a tank, while the BFM works in situ with a test cell directly submerged into the biological tank at similar operational conditions to a typical MBR plant. The mixed liquor of four different MBR units was characterised several times with the three fi ltration methods. The three tested methods seemed to agree in the classifi cation of the tested mixed liquors in terms of fi lterability except for one of the tested activated sludges. Additionally, three critical fl ux protocols were studied using the BFM fi ltration test cell. The fi rst consisted in the classical fl ux-step method, the second included relaxation between fi ltration steps and in the third protocol, 2 min fi ltration at a fi xed fl ux were performed before every fi ltration step. The last protocol was selected as the most representative of full scale MBR operation and the most interesting one for giving valuable information about the irreversibility of the fouling.

Due to their compact design and their high quality and reliable treatment, package or containerised membrane bioreactor (MBR) units are used for decentralised and semi-decentralised wastewater treatment plants. The operational availability, performance and economical viability of these MBR systems depend on the fi ltration performance of the membrane modules. Current chemical cleaning strategies of MBR modules, based on regular (weekly) maintenance cleanings and/or occasional (quarterly to biannual) intensive cleanings proved not to be adapted to semi-central MBR applications (100 up to 1000 p.e.): regular maintenance cleanings require automation and lead to too much care and personnel requirement. Occasional intensive cleanings increase the operational risk of membrane fouling and low cleaning recovery. In addition, semi-central MBR applications are often designed with at least two redundant fi ltration lines. An alternative chemical cleaning strategy was therefore proposed, implemented and assessed in a containerised MBR unit serving a population of about 250 p.e.: at a given time, only one fi ltration line is in operation while the other one soaks in a low-grade chemical solution. The modules are switched alternately on a monthly basis. To identify a cleaning strategy and an agent showing a good recovery, one of the modules was cleaned with H2O2, while the other was cleaned with NaOCl. A cleaning step with citric acid is added when necessary. These cleanings were tested over 16 months with the goal to minimise maintenance effort and chemicals used.

The microbial degradation of pharmaceuticals found in surface water used for artificial recharge is strongly dependent on redox conditions of the subsurface. Furthermore the durability of production wells may decrease considerably with the presence of oxygen and ferrous iron due to the precipitation of trivalent iron oxides and subsequent clogging. Field measurements are presented for oxygen at a bank filtration site in Berlin, Germany, along with simplified calculations of different oxygen pathways into the groundwater. For a twodimensional vertical cross-section, oxygen input has been calculated for six scenarios related to different water management strategies. Calculations were carried out in order to assess the amount of oxygen input due to (1) the infiltration of oxic lake water, (2) air entrapment as a result of water table oscillations, (3) diffusive oxygen flux from soil air and (4) infiltrating rainwater. The results show that air entrapment and infiltrating lake water during winter constitute by far the most important mechanism of oxygen input. Oxygen input by percolating rainwater and by diffusive delivery of oxygen in the gas phase is negligible. The results exemplify the importance of well management as a determining factor for water oscillations and redox conditions during artificial recharge.